Perfluoroalkane fluids have many industrial uses, such as coolants for electronic devices (e.g., supercomputers) and as heat transfer media in vapor-phase soldering processes. However, upon transient heating many of these perfluorinated liquids at high temperatures, toxic impurities may form, such as certain fluoroalkenes, for example perfluoroisobutene (PFIB). These impurities may be hazardous to persons handling the liquid or operating equipment containing the contaminated liquid. Analytical procedures for the identification and quantification of the highly volatile low molecular weight fluorocarbons generally require chromatographic separation and reference standards for calibration. The more toxic perfluoroolefins such as PFIB are not readily available to be used as reference standards and transportation is a serious problem. Marhevka et al., Anal. Chem., 1982, 54, 2607-2610, describe a method to generate a reference standard and suggest the use of an analytical surrogate, perfluorocyclopentene (PFCP), for calibration purposes.
Various methods have been suggested for reducing the hazard of PFIB exposure of operators of equipment that might inadvertently produce PFIB (Turbini, L. J., Zado, F. M., "Chemical and Environmental Aspects of Condensation Reflow Soldering", Electronic Packaging and Production, January, 1980, 49-59 and "Fluorinert Liquids", 3M Publication No. 98-0211-4411-2(78.2)R1 XY, June 1988). Some of these methods include techniques of operating and maintaining vapor-phase soldering equipment to avoid localized super-heating of perfluorinated liquids, thus reducing the amount of PFIB produced, and standards of designing work areas to provide sufficient ventilation to maintain PFIB levels at less than hazardous levels.
U.S. Defensive Publication T983,009 (June, 1979) describes a method of converting PFIB in a mixture of fluorine-containing compounds into a relatively nontoxic ether by contacting the mixture with a solution of methanol and a selected hydrogen halide. While this method does produce products which are generally less toxic than PFIB, it has disadvantages, including 1) being complex to perform in a continuous mode, since various feed streams of reactants must be controlled, 2) using hazardous hydrogen halides (e.g., HF and HCl) as reactants, and 3) yielding products which may create a disposal problem.
U.S. Pat. No. 3,696,156 describes a method of removing perfluoroolefin and perfluorochloroolefin impurities from saturated fluoroperhalocarbon compounds having two to six carbon atoms, by contacting the impure fluoroperhalocarbon in the vapor phase at about 180 to 250 degrees C. with alumina containing a basic alkali metal or alkaline earth metal hydroxide or oxide.
U.S. Pat. No. 5,233,107 describes a process for removing olefinic impurities from hydrogen-containing chlorofluorocarbons in the gas phase at 200 to 400 degrees C. over a zeolite. The contaminated higher boiling chlorofluorocarbons are preheated to convert the liquid to the gas phase in advance. The addition of 0.5 to 10% air or oxygen by volume to the process stream is recommended to keep coking at a very low level.
One of the disadvantages of processes utilizing elevated temperatures is that they require handling hot gases contaminated with hazardous compounds. In addition, certain fluorocarbons are unstable and generate a variety of olefinic and aliphatic impurities at elevated temperatures especially in the presence of catalytic surfaces.
Hall et al. Chemistry and Industry, Mar. 6, 1989, 145-146, describe activated carbon filters to provide protection against exposure to PFIB and note that some of the PFIB is hydrolysed to produce 2H-perfluoroisobutyric acid and hydrogen fluoride. After storage and reuse of the exposed filter, 1,1,3,3,3-pentafluoropropene and 1,1,1,3,3,3-hexafluoropropane were found in the effluent stream.
A system and method for purifying saturated fluoroperhalocarbon liquids by removing olefinic impurities, such as PFIB, therefrom have been disclosed in U.S. Pat. Nos. 5,300,714 and 5,507,941. Inorganic oxide, hydroxide, carbonate, or phosphate particles are used in the method.
England et al., J. Fluorine Chem. 1981, 17, 265-288, describe reactions of amines with a dimer of hexafluoropropene and a perfluorovinyl sulfide prepared from hexafluoropropene. Anhydrous ammonia was added to a solution of hexafluoropropene dimer to form (1-amino-2,2,3,3,3-pentafluoropropylidene)propanedinitrile.
Coffman et al., J. Org. Chem., 1949, 14, 747-753, reported that ammonia reacted with tetrafluoroethylene forms an amine which splits out HF to form difluoroacetonitrile which then forms a trimer.
An organic amine-impregnated activated carbon composition, which preferably has been pre-treated, has been used in breathing gas filters to enhance removal of various toxic perfluorocarbons as is disclosed in U.S. Pat. No. 5,462,908. There is no disclosure as to the composition of the treated material or the nature of the nucleophile used to form a stable immobilized adduct with fluoroalkenes.
An exhaustive review of one of the fluoroalkenes is presented in "The Chemistry of Perfluoroisobutene," by Y. V. Zeifinan, et al., Russian Chemical Reviews, 1984, 53 (March), 256-273. Reactions of PFIB with numerous N, O, S, and P nucleophiles are discussed, without reference to their quantitative analytical application or the ability of these nucleophiles to react with other fluoroalkenes.